A known method for sulfur dioxide removal from waste gas/flue gas is the Sulfacid® process. This process has been especially developed to meet the dual objectives of SO2 removal from waste gases generated by chemical and metallurgical processes and transformation into industrial grade sulfuric acid. It lends itself particularly well to applications where sulfuric acid can be directly used, for example titanium dioxide production or similar sulfuric acid based processes. Additionally, the fixed activated carbon bed is able to remove heavy metals (such as Hg and Cd) from the waste gas.
Typical Waste Gas Inlet Parameters:
SO2 contentup to 1 vol. %Hg content150 μg/Nm3 dryO2 contentmin. 7 vol. %Temperature50-80° C.Dust content<30 mg/m3 STP (all data refers to dry gas)
Typical Clean Gas Outlet Parameters:
SO2 content≤50mg/Nm3 dryHg content25μg/Nm3 dry
The raw gas flows through an activated carbon catalyst fixed bed inside a reactor. The SO2 is converted to sulfuric acid by wet catalysis in the presence of oxygen and water. A water-saturated clean gas is discharged to atmosphere via a stack. The sulfuric acid collected in the pores and on the surface of the catalyst is intermittently washed out by spraying water over the catalyst. Clear industrial grade sulfuric acid of 10 to 50 wt. % strength is collected in a buffer tank. The conversion of sulfur dioxide to sulfuric acid on the catalyst works according to the following reaction equation:SO2+½O2+nH2O ⇒H2SO4·(n−1)H2O+heat
The first Sulfacid® plant was started-up in 1968; now a few hundred plants are in operation worldwide.
It has been found however that the process is less efficient for a higher SO2 concentration in the flue gas. It has been found that using more catalyst does not lead to higher removal of SO2.
EP0 302 224 uses for the removal of SO2 in a gas a catalyst which is hydrophobized by means of hydrophobic polymer compounds such as polytetrafluoroethylene, polyisobutylene, polyethylene, polypropylene or polytrichlorfluorethylen, with a ratio of catalyst:hydrophobizing agent of 25:1 to 1:4.
EP2 260 940 uses for the removal of SO2 in a gas a carbon based catalyst where iodine, bromine or compound thereof is added (ion exchanged or supported) and a water repellent treatment is applied to the carbon based catalyst to enhance the contact between the SO2 gas and the flue gas to be treated, containing SO2.
JPH11 236207 and JP3562551B2 also use a carbon catalyst treated with a water repellent of catalyst to enhance the contact between the SO2 gas and the flue gas to be treated, containing SO2.